Creaming of mixtures of synthetic rubber latices of different average particle sizes



Patented Jan. 10, 1950 CREAMING F MIXTURES or SYNTHETIC RUBBER LATICES OF DIFFERENT Avian- AGE PARTICLE SIZES John S. Rumbold, New Haven, Conn., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application January 11, 1946,

Serial N 0. 640,688

This invention relates to improvements in th creaming of synthetic rubber latices.

Synthetic rubber latices, as is known, may be prepared by the emulsion polymerization in an aqueous medium of butadienes- ,3 or mixtures of butadienes-LS with other polymerizable compounds capable of forming copolymers with butadienes-1,3. Such aqueous emulsion polymerizates, or synthetic rubber latices, may be creamed by the addition of a hydrophilic colloidal creaming agent, such as is used for creaming natural rubber latex, which will cause the dispersion on standing to separate into a polymerrich fraction and a polymer-poor fraction, which fractions may be separated from each other by simple mechanical means, such as decantation, drawing-off, and the like.

By the present invention, there is obtained an increase in the concentration of synthetic rubber in the polymer-rich or cream fraction in the creaming of synthetic rubber latices with bydrophilic colloidal creaming agents.

In carrying out the present invention, a mixture of a plurality of synthetic rubber latices of different average particle sizes is creamed with a hydrophilic colloidal creaming agent. I have discovered that if latices of different average particles sizes are mixed together, the composite latex can be creamed, as with a vegetable mucilage, to a higher solids concentration than the individual constituent latices. Latices of different average particle size may be obtained in several ways. Conventional present-day methods of preparing synthetic rubber latex gives latices of average particle diameter of about .1

micron (from about .07 micron to about .10 micron) measured by the light scattering method, as, for example, with a photo-volt Lumetron calorimeter measuring the intensity of the light scattered at an average angle of 90 to the incident beam. The light scattering method is believed more accurate than the electron microscope method of determining particle size. The electron microscope gives high results which may be ascribed to a slight agglomeration during the drying preparatory to taking the picture, and also possibly to a flattening of the particles during the exposure, due to the rubber globules being pressed down by the electron stream. The average particle size as expressed herein is the diameter of the particle of average volume, and in all cases is measured by the light scattering method. Such conventional synthetic rubber latices of average particle diameter from about .07 to about .10 micron, may be readily ag- 6 Claims. (Cl. 260-851) glomerated to an average particle diameter from about .2 micron up to 1 micron or more without coagulationof the latex by adding a salt to the latex. A mixture of a portion of such conventionally prepared latex having an average particle idameter of about .1 micron with a portion of the same latex agglomerated to an average particle diameter of about .2 micron or higher, will cream to ahigher solids content than either the-original or; the agglomerated latex alone. In general, the difference in average particle diameter of at least two of the constituent latices of the mixture should be at least .05 micron. In using a. conventional present-day commercial synthetic rubber latex as one of the constituent latices of the mixture to be creamed, the average particle diameter of such latex will generally be about .1 micron and the average particle diameter of one or more of the other constituent latices should be at least .15 micron. Another method of obtaining latices of large particlesize is to add a small amount of salt to the original emulsion of the monomeric materials beforepolymerization. One may. then mix the latices made with and Without the addition of salt tothe original emulsion to obtain the high solids content cream by the present invention.

Latices of difierent particle size may also be prepared by varying the conditions of the same agglomerating process, as for example, in the formation of a salt in situ in the synthetic rubber latex. acid, and then alkali added to form a salt in situ. Different average particle size latices may be obtained by varying the length of time after acidification and before addition of the alkali. Different amounts of added stabilizer, and different stabilizers will give latices of different average particle sizes on the incorporation in the latex of the same amount of salt. If desired,

the agglomerating process may be repeated on a previously agglomerated sample to give a latex For example, the latex may be made 3 phase of the synthetic rubber latex, similarly to the creaming of natural rubber latex.

In the preparation of the synthetic rubber latex, as is known, polymerizable monomeric com- 4 A portion of th GR-S latex was aggregated by adding to 1904 parts (wet weight) of the latex 496 parts (wet weight) of an aqueous solution which contained 5.3 parts of ammonium bicarpounds are emulsified in an aqueous medium by 5 bonate, .5 part of sodium lauryl sulfate (commeans of an emulsifying agent, such as a soap or mercial Aquarex D emulsifying and stabilizing other surface active agent, and the polymerizaagent) and 1.6 parts of potassium soap of cocotion is made to take place generally at elevated nut oil acids per 100 parts of total solids of the temperatures in the presence of a catalyst and latex. The thus treated latex was allowed to other regulating materials. Examples of such stand 30 hours at about 25 C., at which time the polymerizable material are the various butadiaverage particle diameter was found to be .20 enes-l,3, for example, butadiene-1,3, methyl-2- micron. The agglomeration was stopped by addbutadiene-1,3 (isoprene), chloro-2-butadiene-L3 ing 139 parts (wet weight) of an aqueous solu- (chlorop-rene), piperylene, 2,3-dimethyl-butadi tion which contained 3.8 parts of potassium hyene-l,3. The polymerizable material as known droxide per 100 parts of total solids of the latex. may be a mixture of such a butadiene-1,3 with The addition of the potassium hydroxide did not another polymerizable compound which is capasignificantly change the average particle diamble of forming rubbery copolymers with butadieter of .2 micron. ems-1,3, for example, up to 70 per cent of such Samples of the original GR-S latex having an mixture of a compound which contains a average particle diameter of .10 micron, and of H the agglomerated latex having an average partiv i T r cle diameter of .20 micron, and of various mixgroup where at least one of the disconnected tures of the original and agglomerated latices valences is attached to an electro-active group, were creamed for one day with ammonium althat is, a group which substantially increases the 95 g te s e Creaming agent over a ran of electrical dissymmetry or polar character of the concentrations of the ammonium alginate to find molecule. Examples of compounds which conthe maximum solids concentrations of the varitain a CH2=C group and are copolymerizable ous creams at the optimum concentration of with butadienes-l,3 are aryl olefins, such as stycreaming agent, mile, and vinyl naphthalene, the alpha meth- The results are shown in the following table:

r Optimum Con- Per ate??? g a t d l'fat e x o? 65g figg ffi g ggig i rgi i i m i Maximum Aver. Part. Aver. Part. creming Creaming, Per (filllgnfiev ggr crgzrrnolliis, li l i cr n l%/l i cr%1 (microns) Phase before e Creaming) 100 o 10 37. 9 it 47. 0 55 .15 34.3 .22 55.6 45 .16 33.5 .23 56.6 35 e5 11 32. s .26 5s. 2 .17 32.5 .21 58.5 0 .20 30.6 .12 39.3

ylene Canboxylic acids, and their esters, nitriles In the creaming of the mixtures as shown in the and amides, such as acrylic acid, methyl acrylate, Ar above table, the average particle diameter of the methyl methacrylate, acrylonitrile, methacrylonimixtures is at least .05 micron greater than the trile, m'ethacrylamide; isobutylene; methyl vinyl average particle diameter of the component latex ether methyl vinyl ketone; vinylidene chloride. 1 of smallest average particle size. Present day commercial synthetic rubbers of the Ewample 7 above types are polymerized chloro-Z-butadiene- 5O v A 36 per cent sol1ds GR-s latex was prepared 1,3 known as neoprene or GR-M rubber, copolymers of butadiene-1,3 and styrene, known as Buna S or GR-S rubber, and copolymers of butadiene-1,3 and acrylonitri'le, known as Buna N or GR-A rubber.

' The following examples are illustrative of the present invention, all parts recited therein being parts by weight:

I Example I A commercial 37.9 per cent solids GR-S latex was prepared by polymerizing an aqueous emulsion of 50 parts of butadiene-1,3 and 50 parts of by polymerizing an aqueous emulsion of '75 parts of butadiene-1,3 and 25 parts of styrene with 5 parts of potassium abietate as an emulsifying agent, 1 part of potassium persulphate and .5 part dodecyl mercaptan in parts of water. The emulsion was polymerized by agitating at 65 C. for 28 hours, after which unpolymerized butadiene was vented off and unpolymerized styrene was removed by steam distillation.

Various samples of the GR-S latex were creamed, using various amounts of ammonium alignate from .1 to .2 per cent based on the water content of the latex. The maximum solids content of. the creams was 47.3 per cent. A portion of the latex was agglomerated with ammonium bicarbonateby adding .2 per cent ammonia and saturating the thus treated latex with carbon dioxide until the pH reached an equilibrium value of 7.2. The thus treated latex was whiter and more opaque than the original latex, show ing the larger particle size by virtue of theagglomerating treatment with ammonium bicarbonate. The latex was further stabilized by the addition of 2 per cent dimethylamine laurate and 75 .3'per cent ammonia, both based on the latex 5 solids; The maximum cream solids of the thus treated latex of larger particle size with various amounts of ammonium alginate as the creaming agentwas 49.7 per cent. A mixture of equal parts of the untreated and treated latices 5 creamed with various amounts of ammonium alginate creaming agent gave a maximum cream solids content of 57.9 per cent, showing a great increase in the solids content of the cream of the mixture over the-solids content of the creams ofthe constituent latices.

6. of ammonia as shown in the table below before passing in carbon dioxide. Inthis way five samples of difierent average particle size were prepared. A composite latex was madeby mixing equal proportions of the five samples. The composite latex and the live differently agglomerated latex samples were creamed with various amounts of ammonium alginate and the maximum cream solids determined in eachcase. The results of the creaming tests are summarizedzin the table below:

APercent CPerceint P r t 1 M mmoma oa u um ercen axlmum, Sam 18 Added g gg fff f Filtered Solids Oon- Cream p (Based on I 1 of G Oil (Based tent at Start Solids, Water on Latex of Oreaming (Percent) Phase) Solids) 1 0.59 7.0 0.7 25.3 48,3 2 .69 7.2 1.0 26.4 51.2 3 .77 7.2, 3.3 24.0 52.6 4 85 7. 4 10. 3 24. 7 53. 4 94 7. 4 12. 0 24. 1 53.0 Composite (E a1 parts of samples Example HIV 2.) It may. readily be seen from the above examples A 33.6 per cent GR-Slatex was prepared by polymerizing an aqueous emulsion of 50 parts of butadiene-1,3 and 50 parts of styrene with2.5 parts of the ammonium soap of coconut oil fatty acids, .3 part ammonium persulphate, .25 part of dodecyl mercaptan, and .1 part of ammonia in 180 parts of Water.

A portion of the above latex was diluted from 33.6 per cent to per cent solids and agglomerated with ammonium bicarbonate by adding .5 per cent ammonia based on the total weight of latex and saturating it with carbon dioxide. The equilibrium pH was 7.2. The latex of increased average particle size thus obtained was stabilized by adding .1 per cent dimethylamine and 3 per cent dimethylammonium laurate based on the solids content, and heated to between 85 and 90 C. by passing steam directly into the latex to decompose and drive ofi the volatile carbonates. A small amount of coagulum formed was filtered off and the latex solids was 24 per cent. The thus agglomerated latex gave a maximum cream solids of 52.6 per cent on creaming with various amounts of ammonium alginate.

A second sample was prepared in the same manner as above but with the addition of .6 per cent ammonia instead of .5 per cent ammonia based on the total weight of latex before saturating with carbon dioxide, thus increasing the concentration of ammonia bicarbonate and hence increasing the average particle size of the latex over that agglomerated on the addition of .5 per cent ammonia followed by the carbon dioxide treatment. This latex had a solids content of 24.6 per cent. On creaming with various amounts of ammonium alginate, a maximum cream solids of 53.4 per cent was obtained.

Equal portions of the two agglomerated latices above were mixed together and creamed with various amounts of ammonium alginate. The maximum cream solids of the mixture was 57.4 per cent, which is considerably higher than the maximum cream solids of either of the component agglomerated latices.

Example IV Samples of the same GR-S latex as was used in Example III were treated in a similar way to those in Example III by adding various amounts that mixtures of latices of different average particle sizes give much higher solids content creams with conventional creaming methods than the component latices of the mixture, 3 V

This application is a continuation-in-part of my application Serial No- 576,139, filed February 3, 1945, now abandoned. v a

In View of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The improvement in the creaming with hydrophilic colloidal creaming agents of synthetic rubber latices comprising aqueous emulsion polymerizates of polymerizable material selected from the group consisting of butadienes-l,3 and mixtures of butadienes-1,3 with up to 70% of said mixture of material which contains a CH2=C group and is copolymerizable with butadienes-l,3 which comprises creaming with a hydrophilic colloidal creaming agent a mixture of such emulsion polymerizates of the same polymerizable chemical material of difierent average particle sizes such that the average particle diameter of the mixture is at least .05 micron greater than the average particle diameter of the component emulsion polymerizate of smallest average particle size, the average particle diameters of the component emulsion polymerizates being from .07 to 1 micron.

2. The improvement in the creaming with hydrophilic colloidal creaming agents of synthetic rubber latices comprising aqueous emulsion polymerizates of polymerizable material selected from the group consisting of butadienes-L3 and mixtures of butadienes-l,3 with up to 70% of said mixture of material which contains a CH2=C group and is copolymerizable with butadienes-l,3 which comprises creaming with a hydrophilic colloidal creaming agent a mixture of one such emulsion polymerizate having an average particle diameter of .07 to .10 micron and another such emulsion polymerizate of the same polymerizable chemical material having an average particle diameter of .2 to 1 micron, the average particle diameter of the mixture of emulsion polymerizates being at least .15 micron.

3.7 The improvement in the crear'ning with vegetable mucilages of aqueous emulsion polymerizates of mixtures of butadiene-l,3 and up to 70% of. said mixture of material which contains a CH2=C group and is copolymerizable with butadene-1,3 Which comprisescreaming with a vegetable mucilage amixture of such emulsion polytables mucilages of aqueous emulsion polymermaterial of difierent average particle sizes such that the average particle diameter of the mixture l is at least .05 micron greater than the average particle diameter of the component emulsion polymerizate of smallest average particle size, the average particle diameters of the component emulsion polymerizates being from .07 to 1 micron.

4. The improvement in the creaming with vegetable mucilages of aqueous emulsion polymerizates of mixtures of butadiene-l,3 and up to 70% of saidmixture of material which contains a CH2=C group andis copolymerizable with butadiene-1,3 which comprises creaming with a vegetable mucilage a mixture of one such emulsion polymerizate having an average particle diameter of .07 to .10 micron and another such emulsion polymerizate of the same polymerizable chemical material having an average particle diameter of .2 to 1 micron, the average particle diameter of the mixture of emulsion polymerizates being at least .15 micron.

5. The improvement in the creaming with vegetable mucilages of aqueous emulsion polymerizates of mixtures of butadiene-l,3 and up to 70% of the mixture of styrene which comprises cream- 7, izates of mixtures of butadiene-l,3 and up to 70% of the mixture of styrene which comprises creaming with a vegetable mucilage a mixture of one such emulsion polymerizate having an average particle diameter of .07 to .10 micron and another such emulsion polymerizate having an average particle diameter of .2 to 1 micron, the average particle diameter of the mixture of emulsion polymerizates being at least .15 micron.

JOHN s. RUMBOLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name 7 Date Willson Sept. 12, 1944 OTHER REFERENCES Pages 33-35 and 41, article by Mueller, India Rubber World, vol. 107, October 1942.

Number Certificate of Correction Patent No. 2,494,002 January 10, 1950 1* JOHN S. RUMBOLD It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 6, for "idameter read diameter; column 7, lines 2, 17, and 31, and column 8, line 11, before aqueous insert synthetic rubber latices comprising; same column 7, line 8, strike out the words and syllable tables mucila-ges of aqueous emulsion polymerand insert instead merizates of the same polymerizable chemical;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 23rd day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant (l'omniasz'oner of Patents. 

1. THE IMPROVEMENT IN THE CREAMING WITH HYDROPHILIC COLLOIDAL CREAMING AGENTS OF SYNTHETIC RUBBER LATICES COMPRISING AQUEOUS EMULSION POLYMERIZATES OF POLYMERIZABLE MATERIAL SELECTED FROM THE GROUP CONSISTING OF BUTADIENES-1,3 AND MIXTURES OF BUTADIENES-1,3 WITH UP TO 70% OF SAID MIXTURE OF MATERIAL WHICH CONTAINS A CH2=C< GROUP AND IS COPOLYMERIZABLE WITH BUTADIENES-1,3 WHICH COMPRISES CREAMING WITH A HYDROPHILIC COLLOIDAL CREAMING AGENT A MIXTURE OF SUCH EMULSION POLYMERIZATES OF THE SAME POLYMERIZABLE CHEMICAL MATERIAL OF DIFFERENT AVERAGE PARTICLE SIZES SUCH THAT THE AVERAGE PARTICLE DIAMETER OF THE MIXTURE IS AT LEAST .05 MICRON GREATER THAN THE AVERAGE PARTICLE DIAMETER OF THE COMPONENT EMULSION POLYMERIZATE OF SMALLEST AVERAGE PARTICLE SIZE, THE AVERAGE PARTICLE DIAMETERS OF THE COMPONENT EMULSION POLYMERIZATES BEING FROM .07 TO 1 MICRON. 